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Mineral Resources > Online Spatial Data > Geology > by state > Maryland Geology

Geologic units in Cecil county, Maryland

Monmouth Formation (Cretaceous) at surface, covers 3 % of this area

Monmouth Formation - Dark gray to reddish-brown, micaceous, glauconitic, argillaceous, fine- to coarse-grained sand; basal gravel in Prince Georges County; thickness 0 to 100 feet.

Lithology: sand; gravel

Potomac Group, including Raritan and Patapsco Formations, Arundel Clay, and Patuxent Formation (Cretaceous) at surface, covers 13 % of this area

Potomac Group - Interbedded quartzose gravels; protoquartzitic to orthoquartzitic argillaceous sands; and white, dark gray, and multicolored silts and clays; thickness 0 to 800 feet. Includes Raritan and Patapsco Formations - Gray, brown, and red variegated silts and clays; lenticular, cross-bedded, argillaceous, subrounded sands; minor gravels; thickness 0 to 400 feet; Arundel Clay - Dark gray and maroon lignitic clays; abundant siderite concretions; present only in Baltimore-Washington area; thickness 0 to 100 feet; and Patuxent Formation - White or light gray to orange-brown, moderately sorted, cross-bedded, argillaceous, angular sands and subrounded quartz gravels; silts and clays subordinate, predominantly pale gray; thickness 0 to 250 feet.

Lithology: gravel; sand; silt; clay or mud

Rancocas Formation (Tertiary) at surface, covers < 0.1 % of this area

Rancocas Formation - Grayish-green and green, silty, glauconitic sand.

Lithology: sand

Magothy Formation (Cretaceous) at surface, covers < 0.1 % of this area

Magothy Formation - White and buff quartz sand with beds of gray and black clayey silt.

Lithology: sand; silt

Volcanic Complex of Cecil County (Late Precambrian (?)) at surface, covers 2 % of this area

Volcanic Complex of Cecil County - Metamorphosed andesitic and dacitic volcanic rocks (greenstone, greenschist, quartz amphibolite, and schistose felsite); amygdules and volcano-clastic textures locally preserved; thickness unknown.

Lithology: greenstone; greenschist; amphibolite; felsic metavolcanic rock

Merchantville Formation (Cretaceous) at surface, covers < 0.1 % of this area

Merchantville Formation - Dark gray to bluish-gray slightly glauconitic, micaceous silty, very fine sand.

Lithology: sand

Wissahickon Formation; Boulder Gneiss (Late Precambrian (?)) at surface, covers 0.4 % of this area

Wissahickon Formation; Boulder Gneiss - (Formerly mapped as Sykesville and Laurel Formations.) Thick-bedded to massive, pebble- and boulder-bearing, arenaceous to pelitic metamorphic rock; typically a medium-grained, garnet-oligoclase-mica-quartz gneiss; locally an intensely foliated gneiss or schist; apparent thickness 15,000 feet.

Lithology: gneiss; schist

Redbank Formation (Cretaceous) at surface, covers < 0.1 % of this area

Redbank Formation - Reddish-brown, slightly micaceous and glauconitic, fine to medium sand.

Lithology: sand

Ultramafic rocks (Probably lower Paleozoic) at surface, covers 0.1 % of this area

Ultramafic rocks - Includes serpentine, steatite, and other products of alteration of peridotites and pyroxenites.

Lithology: serpentinite; pyroxenite; peridotite

Mt. Laurel-Navesink Formation (Cretaceous) at surface, covers < 0.1 % of this area

Mt. Laurel-Navesink Formation - Dark greenish brown and dark gray, highly glauconitic sandy silt and silty sand.

Lithology: silt; sand

Potomac Formation (Cretaceous) at surface, covers < 0.1 % of this area

Potomac Formation - Variegated silts and clays with beds of quartz sand.

Lithology: silt; clay or mud; sand

Pamunkey Group; Aquia Formation (Paleocene) at surface, covers 0.8 % of this area

Pamunkey Group; Aquia Formation - Dark green to gray-green, argillaceous, highly glauconitic, well-sorted fine- to medium-grained sand; locally indurated shell beds; thickness 0 to 100 feet.

Lithology: sand

Wissahickon Schist (Paleozoic) at surface, covers < 0.1 % of this area

Wissahickon Schist - Dense micaceous schist, gneiss and migmatite.

Lithology: mica schist; gneiss; migmatite

Matawan Formation (Cretaceous) at surface, covers 1 % of this area

Matawan Formation - Dark gray micaceous, glauconitic, argillaceous, fine-grained sand and silt; absent in outcrop southwest of Patuxent River; thickness 0 to 70 feet.

Lithology: sand; silt

Wenonah Formation (Cretaceous) at surface, covers < 0.1 % of this area

Wenonah Formation - Gray and rust-brown fine to medium, micaceous, sparingly glauconitic quartz sand.

Lithology: sand

Upland Deposits (Eastern Shore) (Quaternary) at surface, covers 26 % of this area

Upland Deposits (Eastern Shore) - Gravel, sand, silt, and clay. Mostly cross-bedded, poorly sorted, medium- to coarse-grained white to red sand and gravel; boulders near base; minor pink and yellow silts and clays; (Wicomico Formation of earlier reports); thickness 0 to 90 feet, locally thicker in paleochannels.

Lithology: gravel; sand; silt; clay or mud

"Glenarm Wissahickon" formation (Probably lower Paleozoic) at surface, covers 0.1 % of this area

"Glenarm Wissahickon" formation - Lithologically similar to oligoclase-mica schist of the Wissahickon Formation (PZw), but also includes lenticular amphibolite bodies having ocean-floor basalt chemistry.

Lithology: mica schist; mafic gneiss; amphibolite;

Metagabbro and Amphibolite (Early Paleozoic (?)) at surface, covers 8 % of this area

Metagabbro and Amphibolite - Weakly to strongly lineated metagabbro and epidote amphibolite.

Lithology: gabbro; amphibolite

Port Deposit Gneiss (Paleozoic) at surface, covers 12 % of this area

Port Deposit Gneiss - Moderately to strongly deformed intrusive complex composed of gneissic biotite quartz diorite, hornblende-biotite quartz diorite, and biotite granodiorite; all rocks foliated and some strongly sheared; age 550 +/- 50 m.y. * by radiogenic dating.

Lithology: granitic gneiss; quartz diorite; granodiorite

Peters Creek Schist (Probably lower Paleozoic) at surface, covers < 0.1 % of this area

Peters Creek Schist - Chlorite-sericite schist containing interbedded quartzite.

Lithology: schist; quartzite

Lowland Deposits (Quaternary) at surface, covers 7 % of this area

Lowland Deposits - Gravel, sand, silt, and clay. Medium- to coarse-grained sand and gravel; cobbles and boulders near base; commonly contains reworked Eocene glauconite; varicolored silts and clays; brown to dark gray lignitic silty clay; contains estuarine to marine fauna in some areas (includes in part Pamlico, Talbot, Wicomico and Sunderland Formations of earlier reports); thickness 0 to 150 feet.

Lithology: gravel; sand; silt; clay or mud

Amphibolite (Paleozoic) at surface, covers < 0.1 % of this area

Amphibolite - amphibolite

Lithology: amphibolite

Upland Deposits (Western Shore) (Quaternary) at surface, covers 2 % of this area

Upland Deposits (Western Shore) - Gravel and sand, commonly orange-brown, locally limonite-cemented; minor silt and red, white, or gray clay; (includes Brandywine, Bryn Mawr, and Sunderland Formations of earlier reports); lower gravel member and upper loam member in Southern Maryland; thickness 0 to 50 feet.

Lithology: gravel; sand; silt; clay or mud

Ultramafic Rocks (Early Paleozoic - Late Precambrian (?)) at surface, covers 1 % of this area

Ultramafic Rocks - Chiefly serpentinite with partly to completely altered dunite, peridotite, pyroxenite, and massive to schistose soapstone; talc-carbonate rock and altered gabbro are common in some bodies.

Lithology: serpentinite; dunite; peridotite; pyroxenite; gabbro

Wissahickon Formation (Undivided) (Late Precambrian (?)) at surface, covers 11 % of this area

Wissahickon Formation (Undivided) - Muscovite-chlorite-albite schist, muscovite-chlorite schist, chloritoid schist, and quartzite; intensely folded and cleaved.

Lithology: schist; quartzite

Banded mafic gneiss (Precambrian) at surface, covers 0.1 % of this area

Banded mafic gneiss - Dark, fine to medium grained; includes rocks of probable sedimentary origin; may be equivalent to "PZmgh."

Lithology: mafic gneiss; paragneiss

Magothy Formation (Cretaceous) at surface, covers 0.5 % of this area

Magothy Formation - Loose, white, cross-bedded, "sugary", lignitic sands and dark gray, laminated silty clays; white to orange-brown, iron-stained, subrounded quartzose gravels in western Anne Arundel County; absent in outcrop southwest of Patuxent River; thickness 0 to 60 feet.

Lithology: sand; clay or mud; gravel

Wissahickon Formation; Metagraywacke (Late Precambrian (?)) at surface, covers 0.1 % of this area

Wissahickon Formation; Metagraywacke - (Formerly mapped as Peters Creek Formation.) Rhythmically interbedded chlorite-muscovite meta-graywacke and fine-grained chlorite-muscovite schist; graded bedding locally preserved; thickness probably 2,000 to 3,000 feet.

Lithology: metasedimentary rock; schist

Baltimore Gabbro Complex (Late Precambrian (?) - Early Paleozoic ) at surface, covers 6 % of this area

Baltimore Gabbro Complex - Hypersthene gabbro with subordinate amounts of olivine gabbro, norite, anorthositic gabbro, and pyroxenite; igneous minerals and textures well preserved in some rocks, other rocks exhibit varying degrees of alteration and recrystallization with a new metamorphic mineral assemblage.

Lithology: gabbro; norite; pyroxenite

Unit B (Cretaceous-Tertiary) at surface, covers < 0.1 % of this area

Unit B - Greenish-gray sandy and clayey glauconitic silt.

Lithology: silt

Port Deposit Granodiorite (Paleozoic) at surface, covers < 0.1 % of this area

Port Deposit Granodiorite - granodiorite

Lithology: granodiorite

Unit C (Tertiary) at surface, covers < 0.1 % of this area

Unit C - Grayish-green, clayey glauconitic silt and sand.

Lithology: silt; sand